1. Field of the Invention
The present invention relates to forming electrical connectors in an insulating host, and more particularly, to forming arrays of spring elements in a flexible polymer sheet.
2. Background of the Invention
Conventional electrical connectors used to connect components such as printed circuit boards are fabricated using a wide variety of techniques. A common approach is to use stamped metal springs, which are formed and then individually inserted into an insulating carrier to form an array of electrical connection elements. Other approaches to making electrical connectors include using anisotropically conductive adhesives, injection molded conductive adhesives, bundled wire conductive elements, and small solid pieces of metal.
As the desire for device performance enhancement drives packaging technology to shrink the spacing (or the pitch) between electrical connections (also referred to as a “leads”), a need exists to shrink the size of individual connector elements. At the same time, the total number of connections per package is increasing. For example, existing integrated circuit (IC) packages may be built with a pitch of 1 mm or less with 600 or more connections. Furthermore, IC devices are designed to be operated at increasingly higher frequencies. For example, IC devices for use in computing, telecommunication, and networking applications can be operated at a frequency of several GHz. Operating frequencies of the electronic devices, package size, and lead count of the device packages thus place stringent requirements on the interconnect systems used to test or connect these electronic devices.
In particular, the mechanical, electrical, and reliability performance criteria of an interconnect system are becoming increasingly demanding. Electrical and mechanical reliability specifications for use with high speed, small dimension and large pin count IC devices can place requirements that conventional interconnect technologies described above cannot easily fulfill. In general, conventional connector systems optimized for electrical performance have poor mechanical and reliability properties, while connector systems optimized for mechanical performance and improved reliability have poor electrical characteristics.
A particular problem encountered by today's interconnect systems is non-coplanarity of leads in the electronic components to be connected. Coplanarity of elements in a planar package exists, for example, when those elements reside within a common reference geometrical plane. In a conventional package, factors that can contribute to non-coplanarity of connector elements (or leads) of the package include manufacturing variability and substrate warpage. For conventional connector elements arranged in an array, coplanarity variation across a package may exceed vertical tolerances for connector elements, resulting in failure of electrical connection in some elements.
Coplanarity problems are not limited to IC packages, they may also exist in a printed circuit board (PC board) to which these IC packages are attached. Coplanarity problems may exist for land grid array pads formed as an area array on a PC board due to warpage of the PC board substrate. Typically, deviation from flatness in a conventional PC board is on the order of 75 to 125 microns or more per inch.
Additionally, the deviations from planarity in circuit boards, packages, and other components in which arrays of electrical connectors are employed, often may not scale down as other dimensions, such as array spacing and connector size, decrease. Thus, for example, large vertical deviations in positions of contacts may occur even for circuit boards or other components that have smaller pitch. For conventional connectors having pitch of less than about 2 mm between connector contacts, it becomes more difficult as the pitch decreases to produce elastic contacts that can compensate for such coplanarity deviations and still realize acceptable electrical contact properties, such as low resistance and low inductance.